In general, an imaging apparatus such as a digital camera or a camera mounted on a mobile phone performs an imaging process by forming an image of a subject on a two-dimensional imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). Recently, in some cases, a technique called wavefront coding (WFC) has been employed in the imaging apparatus.
Now, an imaging apparatus employing the WFC technique will be described with reference to FIG. 10. FIG. 10 is a schematic diagram illustrating an optical system of the imaging apparatus employing the WFC technique in the related art. As illustrated in FIG. 10, the imaging apparatus in the related art includes an optical system 90 and an imaging element 95. Lenses 91 to 93 and a phase plate 94 which is an optical wavefront coding element are disposed in the optical system 90.
In the example illustrated FIG. 10, in the case where there is no phase plate 94, the lenses 91 to 93 allows the light emitted from the subject which is to be imaged to converge. On the other hand, as illustrated in the example of FIG. 10, the phase plate 94 is disposed, so that the phase plate 94 regularly disperses the light flux emitted from the subject which is to be imaged to deform the image formed on the light receiving surface of the imaging element 95. Therefore, the imaging element 95 obtains an image (hereinafter, referred to as an “intermediate image”) in the state where a focus thereof is deviated. Next, the imaging apparatus applies a digital process such as an inverse filter to the intermediate image formed by the imaging element 95 to generate an image of the subject.
In the case where relative positions between the imaging apparatus and the subject are changed, the intermediate image obtained by the imaging apparatus employing the WFC technique has a small amount of change in blur degree. For example, the intermediate image in the case where the distance between the imaging apparatus and the subject is H1 and the intermediate image in the case where the distance between the imaging apparatus and the subject is H2 (>H1) have a small amount of change in blur degree. The imaging apparatus employing the WFC technique generates the subject image by applying a digital process to the intermediate image having a small amount of change in blur degree, so that it is possible to increase the depth of field.    Patent Literature 1: Japanese Laid-open Patent Publication No. 2008-109542    Patent Literature 2: Japanese Laid-open Patent Publication No. 2003-235794    Non-Patent Literature 1: Edward R. Dowski, Jr. and W. Thomas Cathey, “Extended depth of field through wave-front coding”, Applied Optics, vol. 34, no 11, pp. 1859-1866, April, 1995.